Droplet actuators are used to conduct a wide variety of droplet operations. A droplet actuator typically includes a substrate associated with electrodes for conducting droplet operations on a droplet operations surface thereof and may also include a second substrate arranged in a generally parallel fashion in relation to the droplet operations surface to form a gap in which droplet operations are effected. The gap is typically filled with a filler fluid that is immiscible with the fluid that is to be subjected to droplet operations on the droplet actuator.
In some applications of a droplet actuator there is a need for using “beads” for various assays. For protocols that make use of beads, the beads are typically used to bind to one or more target substances in a mixture of substances. The target substances may, for example, be analytes or contaminants. There is a need for an efficient approach to bead washing on a droplet actuator in order to reduce the amount of one or more substances in a bead-containing droplet that may be in contact with or exposed to the surface of the bead or beads.